Vintage Mustang- 4 to 5-Lug Nut Conversion

You can always spot a straight-six Mustang with a quick look at the wheels. Every V8 Mustang that came out of Ford in the early days had five lug nuts, the 6-cylinder cars got four. The suspension and steering under the 6-bangers is not as stout, even the rear end was smaller the 7 3\4” unit. This leaves the 6-cylinder Mustang owner in a pickle. Since the standard 5 on 4 1\2” bolt pattern is so widely used, wheel selection is much greater than the less-popular 4 lug pattern. Strength is another issue. While the extra lug does add some strength, the rear differential is considerably smaller and won’t last long behind V8 power. Since chances are the 6-banger project you are working on needs some fresh joints and brakes anyway, why not replace it all together and go 5-lug.

You should recognize the ’65 Mustang from last month’s issue where we swapped out the suspension components with fresh suspension consumables from Mustang Depot. We also upgraded to V8 coil and leaf springs and a bigger front sway bar as part of the Mustang Depot’s Stage 1 Ultra Suspension kit. This kit used the optional lowered springs, which dropped the Mustang an inch, front and rear, for a better stance and to get rid of the 4×4 look. During this swap, we upgraded to 5-lug V8 brakes and steering, which we are detailing here.

Swapping to V8 front spindles is simple enough, but you can’t just swap spindles and drums. The steering linkages are all different. The I-6 tie-rod ends do not fit the V8 spindles and neither does anything in between, so it all has to go. We sourced all the steering components, from the steering pitman arm and idler arm to the tie rod ends from Mustang Depot. All of the components used were Scott Drake-branded, which is top-shelf quality, so we knew we could trust them on our project.

For brakes, we ditched the drums and went with a set of Stainless Steel Brakes 4-piston disc brakes. The kit we used is the A120-20, which comes with a power-assisted (7” booster) dual-bowl master cylinder, 11.25” vented rotors with Xtra-life plating and the all important 5 on 4.5” bolt pattern. These low-profile 4-piston calipers work with most 14” wheels, so you don’t have to go up to 17” wheels like many of the other disc brakes, which is perfect for us since we are building a classic-themed Pony. The power option relegates the Mustang to an automatic transmission, unless you go with a remote-mount hydraulic clutch, but that will complicate things even more, so the slush-box will stay in our car.

We didn’t want to swap V8 parts up front and leave the weak 7 3\4” rear diff out back so we sourced a good 8” rear from a local salvage yard. The 302 that will sit between the fenders of this Mustang will be slightly warmed over, but nothing the 8” can’t handle. As 9” rears are getting harder to find and budget is always a concern, we went for the cheaper and more plentiful 8”. For less than $100, we had a solid rear with good drum brakes that would handle the power. As you saw last month, we replaced the leaf springs with a V8 leaf pack. The rear end is an easy swap but you need a few new parts and have to make some mods. One thing we did not cover here was the driveshaft. We picked up a V8 driveshaft at the same salvage yard as the rear end, but are waiting to install it when the 302 goes in. The u-joints are different sizes from the 7 3\4” rear to the 8” unit, by a considerable margin, so factor a driveshaft into your swap.

By the time the Mustang was back on the ground, we had spent about three days (a week and a half in magazine time, but that is because taking pictures really slows you down) with two guys working on the car most of the day. We had to make a couple of trips to the parts store too. Once it was done, is was all worth it. 5 lugs and disc brakes, everything you need.

01. We set the car up using jackstands to support the car. You have to work on both sides of the car at the same time, so the entire front end needs to be off the ground. NEVER work on a car using just a jack, always use quality jackstands.

02. First, we pulled the steering components. The pitman arm is difficult to remove, even with a puller. You can rent these from your local parts store if you don’t own one, but this one puller works great for tie-rod ends and ball joints too.

03. We were replacing the entire suspension but if you just want to add disc brakes, you don’t have to replace everything. The upper arms and lower arms can be reused with the V8 spindles. We pulled it all.

04. After the new lower arm was installed, the new spindles we picked up from Stainless Steel Brakes were installed. You can use Granada spindles as well, but that requires different brakes. Since the factory V8 spindles are available in remanufactured form, we kept it all Mustang. These spindles were shipped cast gray, so we sprayed them black to keep the rust away. The castle nuts were torque to spec- 70 ft lbs top and bottom.

05. We pre-assembled the steering links. We didn’t get any directions on how this goes together because each part is separately packaged. A little research on the web and we had it right. The tie-rod sleeves were threaded an equal amount on both inner and outer, left to right.

06. First we installed the tie-rod ends, but did not torque them yet.

07. Then the new pitman arm went on. The key here is to ensure the steering spindle is centered so the wheel will be in the correct position when the car is driving straight. This done by counting wheel turns lock to lock and then splitting that number and setting the wheel. The pitman arm nut requires a lot torque, 85-110 ft lbs.

08. The tie rod sleeves will get their final adjustment at the alignment shop, but if you plan on driving the car to the shop, you need a baseline. We used a measuring tape to set the spindles straight, with no toe-in. This won’t handle well, but our alignment shop is about 5 miles away. Each side must be threaded an equal amount. The sleeve lock collars were torqued to 20 ft lbs.

09. We packed the bearings by hand with some moly grease. You can use a bearing packer too. We then installed the inside bearings and seal to the rotor.

10. We also applied a generous amount of grease to the spindle itself. Wearing gloves makes for quick clean up. We also installed the backing plates.

11. The rotor was installed to the spindle. The proper mounting method is to rotate the rotor while loosening and tightening the spindle nut. This helps seat the bearings to the spindle. You want the rotor to spin freely, but not be loose. Don’t forget the washer between the nut and the bearing.

12. The caliper uses a stainless steel plate on the top to retain the brake pads. You can install the pads before or after you mount the calipers.

13. The calipers were installed using the supplied hardware. The caliper face the front of the car, not the rear like most disc brake kits.

14. Next we torqued the front suspension components to spec. Each tie-rod was set to 40 ft lbs.

15. The last step on the front brakes was replacing the old rubber lines. The SSBC brake kit comes with new rubber lines that mount to the original steel line. Make sure you use a line wrench, otherwise you will round-off the nut and have to replace it.

16. Before we could set the car back on the ground, we had to bolt on the wheels. We bought a set of new McGard lug nuts and wheel locks for the Cragar Street Lite wheels, which had been powder coated flat black for an aggressive look.

17. Now the Mustang has 5-lug and disc brakes up front, but we are not done yet, the back end needs to come off the ground. All four wheels were wrapped in BF Goodrich Radial TA rubber, 15” out back and 14” up front, for that classic look with the black powder coat Cragar Street Lite wheel.

18. With the rear of the Mustang on jackstands, we removed the driveshaft, E-brake cables and brake line.

19. Then we released the tension on the rear springs so the rear would hang low, you don’t want any tension on the rear end when you unbolt the springs.

20. Using an impact gun, the U-bolts were removed. One nut was really stubborn, so we ended up cutting one U-bolt with a sawzall. We had the springs and rear out of the car when we did this because we were replacing the springs, but you can do it under the car just as easily.

21. We reused the original U-bolt plates, but as you can see here, the original holes were for the smaller diameter U-bolts. We used a plasma cutter to slot the holes. You could also drill them out.

22. The 8” rear was slid in place and the new U-bolts were mounted to the plates. We picked up our U-bolts from the local parts store, but had to wait a few days as they only had 2 in stock. These need to be torque to 40 ft lbs.

23. Under the dash, the master cylinder lever was removed from the brake pedal. This can be tricky as it is a tight fit, but be patient, it will come off.

24. We mounted the new power booster to the firewall. There is some trial and error fitment here and the nuts are hard to get to. We used a 9\16” distributor wrench, which was slow, but effective. Our ratcheting wrenches wouldn’t fit. We also removed the tower brace for better access.

25. Using some steel wire, we made a template for the brake lines and bent the supplied lines to match. Be patient and take your time, a kinked line is no good.

26. Then the lines were installed. The front bowl feeds the original distribution block which feeds both front calipers; we used the supplied plug to block off the rear brake line outlet on the block. The rear bowl feeds the rear drum brakes and runs through an adjustable proportioning valve. This allows us to tune the amount brake bias so the rear brakes don’t lock up before the fronts. All that is left now is to bleed the brakes and we are done.

A life-long gearhead, Street Tech Magazine founder and editor Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 5 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced. You can follow Jefferson on Facebook (Jefferson Bryant), Twitter (71Buickfreak), and YouTube (RedDirtRodz).